running water out of old well

I have a drilled well, 1hp 12 gpm pump at 240' and let it run from faucet at wellhead, trying to get clear water. It ran dry after after 20 min or so and water was still very dirty. The faucet is definetly putting out more than 12 gal. per min, closer to 20 gpm....is this pumping water too fast, causing dirt or whatever to be pulled into water?? Also, how long is too long to let pump run after water stops pumping, any?? I have to make it about 400' to shut off pump unless someone is there with me. thanks

First off, the static height of the water is as important a factor as the depth of the pump. It determines both the storage capacity and the height the pump needs to lift. The storage capacity determines how many gallons you can pull before the well's recovery rate becomes an issue.

When my mud well was put in, the well driller left his 5 GPM running for days, both to get it to run clear, and to satisfy the mortgage lender that there was adequate GPM of recovery. When I put my 10 GPM pump in the well, it immediately turned muddy and actually sucked mud up into the pump.

Now, I assume at 240 feet that your well is drilled in rock and that eventually it will run clear. A 12 GPM pump with no pressure (depending on the size of the wellhead faucet) could pump more than 12 GPM but if you are pumping the well dry, that is eventually a column of 240 feet of water the pump needs to lift. With every 2.31 feet equal to 1 PSI, that's around 100 PSI down at the pump. Surely that should regulate the GPM down to something the well can recover from. Did the driller's report state the GPM the well is capable of?

20 minutes at 20 GPM is 400 gallons stored in the well. That is pretty good. Wait exactly one hour and do it again. Time how long it takes and how much water you get out of the well the second time. Then wait 30 minutes and do it again. The amount of water you get out, divided by the number of minutes it took, will give you a good indication of your recovery rate.

If you run more water than the recovery rate, you will always pump the well dry. You can try to choke the pump back to the recovery amount and it should run steady as long as you want. However, the recovery flow rate may not be enough to help clean out the well. What you are doing is probably the best way to clean out the well. Run it hard until it pumps off, wait 30 minutes or an hour, and do it again. If you can get to the kill switch within about a minute after the well pumps dry, you won’t hurt the pump. It is still in water and has water in it, so it takes a few minutes to start heating up.

The slower the recovery rate, the longer it takes to clean up a well. I have a well that makes a little less than 1 GPM. When I shock the well and try to clean it out, it takes many days. I use a Cycle Sensor to shut off the pump when the well is dry. Then I set it to automatically restart in an hour. It pumps out about 50 gallons, is off for an hour, then does it again. After a couple of days it clears up nicely.

How many gallons in 240 feet of casing? I guess it depends on casing size and how much the pipe and wiring displaces but I wild-ass-guess around a gallon per foot for a 6 inch casing so either the well recovery is pretty good or the GPM is dropping off as the level drops.